PROJECT SUMMARY/ABSTRACT More than 35 million people worldwide are living with HIV-1 and nearly half this population suffers from HIV- mediated CNS impairments, collectively known as HIV-associated neurocognitive disorders (HAND). This is partly because HIV-1 can persist in viral reservoirs harbored by certain CNS cell populations, chiefly microglia, despite the use of antiretroviral therapy. These infected and/or activated cells release neurotoxic viral proteins, such as transactivator of transcription (Tat) and a variety of pro-inflammatory factors such as CCL5, upregulating neuroinflammation and resulting in sublethal and lethal neuropathology that are worsened in the context of opiate drug abuse. This proposal aims to take a closer look at the CCL5-CCR5 signaling axis in mediating this interaction, which based on previous studies is suggested to be critical in HIV neuropathology, and can be further dysregulated upon exposure to morphine. CCR5 is a co-receptor for HIV entry, but also may be independently involved in promoting glial activation and migration to create a damaging environment for nearby neurons. This proposal will employ in vitro and in vivo HIV-1 Tat models to test the hypothesis that CCR5 is a point of convergence for interactive Tat and opiate-induced neurotoxicity in two overarching aims. In the first aim, neuronal survival will be measured in a series of repeated measure studies conducted on co- cultures of mixed glia and neurons from C57Bl/6 and/or CCR5 global knock-out mice, treated with Tat morphine. Preliminary findings confirm that morphine worsened Tat-induced toxicity in wild-type co-cultures; substitution of CCR5-null glia significantly reduced the loss of wild-type neurons, implying a net neuroprotective effect. Therefore, a second sub-aim will investigate a mechanism by which blocking CCR5 activation may permit neuronal survival. Specifically we test whether Tat morphine alters levels of the well-known neurotrophin BDNF, whose levels and processing from proBDNF are modulated by morphine and correlate inversely with cognitive deficits in patients. This sub-aim will utilize molecular techniques and protein analysis to measure changes in BDNF and proBDNF expression and signaling upon exposure to Tat morphine treatments in primary cultures with and without CCR5. In Aim 2, parallel whole-animal studies in global CCR5 knockout mice crossed with Tat-inducible transgenic mice will reveal functional consequences of CCR5 loss on CNS cells upon long-term Tat exposure. This will be achieved through a number of behavioral assays designed to measure anxiety, motor skills, and cognition ? three areas of neurologic decline seen in HAND. Additional tests using morphine-treated groups will be conducted to support in vitro evidence of the importance of CCR5 in driving Tat morphine-mediated neuronal damage. In a final sub-aim, brains from mice that have completed behavioral tests will be harvested and analyzed for neuron morphology, glial activation, and markers of inflammation in regions selectively vulnerable to HIV/viral proteins and drugs of abuse, such as the striatum and hippocampus. Correlative analyses will link altered behaviors with changes in tissue parameters.